Planet facing 'catastrophe' - Brown

Mr Brown said letting the emissions which cause global warming run unchecked would have massive economic, human and environmental costs.

He warned that ignoring emissions would leave the UK facing a future of killer heatwaves, floods and droughts.

In a speech to 17 leading nations meeting in a bid to make progress towards agreeing a new treaty on climate change at UN talks in December, he warned of the "heavy price" of failure - with no Plan B for the planet if negotiations collapse.

Failing to tackle climate change would have an economic impact worse than that of the two world wars and the Great Depression, he said, but action could provide economic opportunities in green jobs and technology.

He told the Major Economies Forum - gathered in London for talks which aim to narrow the gap between different countries on areas of dispute ahead of the climate summit in Copenhagen - that a deal was possible.

But with less than two months to go before the crunch UN conference, he warned countries were not making progress quickly enough to reach agreement and urged leaders to step in to break the impasse.

He said heads of state should work together directly to secure a deal with binding targets for rich countries to cut their emissions in the coming decades, action by developing nations and funding to help the poorest countries cope with the impact of climate change.

The Prime Minister's warning over the consequences of failure were welcomed by environmental groups, who want rich countries primarily responsible for the greenhouse gases in the atmosphere to take the lead in signing up to tougher emissions cuts.

But opposition MPs and some campaigners criticised the gap between Mr Brown's rhetoric and the Government's policies on airport expansion and new polluting fossil fuel power plants.